Tuning The Triple-Phase Boundary Of Gas Diffusion Electrodes For Electrocatalytic Reduction Of Carbon Dioxide To Ethylene

Ethylene（C₂H₄）has attracted widespread attention due to its wide application（such as plastics,fibers,and ripening agents）and ultra-high production capacity（more than 200 megatons per year）.Since traditional industrial ethylene production faces shortcomings such as high energy consumption and high carbon emissions,it is urgent to develop new approaches that can synthesize ethylene at a sustainable and carbon-neutral manner.Electrocatalytic reduction of carbon dioxide（ECO₂RR）is a promising route for ethylene synthesis because this reaction uses renewable energy as the driving force,operates at room temperatures and ambient pressures,can efficiently capture and convert CO₂,which can potentially alleviate the greenhouse effect,and,most importantly,employs the cheap and earth-abundant copper-based materials as electrocatalysts.At present,most studies on electrocatalytic reduction of CO₂ to C₂H₄ use H-type cell as the reactor,but its reaction rate is limited by slow mass transport,with ethylene-evolving current densities not exceeding 50 m A/cm².Compared to H-cell,flow cell enables ethylene production at industrial-scale current densities greater than 200 m A/cm².At present,one bottleneck lying in the pathway of CO₂electroreduction to C₂H₄ is the low ethylene selectivities at high current densities.Although strategies such as cell structure design,electrolyte regulation,ion exchange membrane modification,and catalyst optimization have been widely used to improve this reaction,achieving ethylene selectivity of more than 60%remains challenging.The key to achieving industrial-grade current density in flow cell lis in that the gas diffusion electrode（GDE）can form a solid/liquid/gas boundary among copper nanoelectrocatalysts,electrolytes,and CO₂ gas.This interface can accelerate the transport of CO₂,protons,and electrons,therefore enabling ECO₂RR–to–C₂H₄electrocatalysis at high current densities.In this paper,the following works are carried out with a goal of tuning the triple-phase boundary of GDEs to improve ECO₂RR–to–C₂H₄performance:（1）First,a layer of polytetrafluoroethylene（PTFE）is modified onto the hydrophobic carbon fiber surface of GDE to improve the ability of carbon-carbon coupling over the triple-phase boundary.On the one hand,the modification of PTFE increases the hydrophobicity and robustness of the carbon fiber framework of GDE,extending the ECO₂RR operational lifetime at high current densities beyond 100 hours.On the other hand,the modified PTFE reduces the exposure percentage of the interstice among carbon fibers to construct a local confinement field between the triple-phase interface and the hydrophobic carbon fiber that can confine the generated*CO to improve the coverage of*CO intermediate and,consequently,to reduce the energy barrier required for carbon-carbon coupling,with which*CO dimerize easily into C₂H₄.The resulting PTFE-modified GDE achieves a C₂H₄ Faraday efficiency of 85.9%at an applied current density of 400 m A/cm².（2）Based on these results,the subsequent work further improves the amout and inherent carbon-carbon coupling ability of triple-phase boundary by combining ionomer modification with electrochemical reconstruction.First,copper phosphate microspheres assembled by ultrathin nanosheets were synthesized by a wet chemical method,and then serve as precatalyst to craft three-dimensional loosely-connected Cu nanoparticles by precise control over ionomer modification and reconstruction kinetics.Hydrophobic functional groups of the ionomer can assist CO₂ diffusion,while its hydrophilic functional groups offer channels for transporting ions and water.This unique transport property can effectively increase the number of triple-phase boundary.In addition,the reconstructed copper nanoparticles feature abundant vacancies and facet junctions,merts that can enhance the inherent catalytic ability of the triple-phase boundary of GDE toward ECO₂RR to generate C₂H₄ in a low-energy reaction pathway.For these reasons,the GDE modified with both ionomer and copper phosphate derivate,when applied with 1000 m A cm^-2 current density,can deliver a 72%C₂H₄ selectivity.